[Haskell-cafe] [GHC 7.8.4] IO Monad leak space?

[Tom Ellis]

Probably easiest to just use the ghc-core package:

    http://hackage.haskell.org/package/ghc-core

On Fri, Jul 03, 2015 at 10:19:14AM -0700, Dan Burton wrote:
> It can, if you know the correct magic incantations to give ghc (which I
> don't, but I know the knowledge is out there). The phrase to Google is
> "reading ghc core", where "core" refers to an intermediate language that
> still resembles Haskell.
> 
> On Friday, July 3, 2015, Stefan Reich <
> stefan.reich.maker.of.eye at googlemail.com> wrote:
> 
> > Here's a general question: Can the output of the Haskell compiler be
> > inspected in some - readable - way?
> >
> > Stefan
> >
> > On Fri, Jul 3, 2015 at 10:18 AM, Baojun Wang <wangbj at gmail.com
> > <javascript:_e(%7B%7D,'cvml','wangbj at gmail.com');>> wrote:
> >
> >> Hi,
> >>
> >> First of all, I found it interesting that
> >>
> >> loopM_ f k n s = when (k <= n) (f k >> loopM_ f (s+k) n s)
> >>
> >> loopM_ seems faster than mapM_    ( mapM_ f [k, k+s..n]))
> >>
> >> I think mapM_ is used very commonly, why it's performance is even lower
> >> than a hand-written loop function?
> >>
> >> 2nd, even I replace mapM_ with loopM_ from above, when chain IO action,
> >> it still can leak space. ( Because IO Monad (>>) need keep ``RealWorld s''
> >> updated so that I/O actions can be done in-order? )
> >>
> >> Consider below function:
> >>
> >> f3 :: UArray Int Int -> IOUArray Int Int64 -> Int -> IO ()
> >> f3 u r i = let !v = u ! i
> >>             in go (f31 v) i i
> >>   where f31 v j = readArray r j >>= \v1 ->
> >>           writeArray r j (v1 + (fromIntegral i) * (fromIntegral v))
> >>         f31 :: Int -> Int -> IO ()
> >>         go g k s = when (k <= maxn) (
> >>           g k >> go g (s+k) s )
> >>
> >> When call f3:
> >>
> >>   loopM_ (f3 uu res) 1 1 1000000
> >>
> >> Which will have blow profiling output:
> >>
> >> individual inherited
> >> COST CENTRE MODULE no. entries %time %alloc %time %alloc
> >>
> >>
> >> ...
> >> loopM_ Main 104 4000002 7.4 10.1 100.0 99.3
> >> f3 Main 113 1000000 1.0 2.0 70.2 69.1
> >> f3.go Main 116 14970034 32.7 67.1 68.8 67.1
> >> f3.f31 Main 117 13970034 34.5 0.0 36.1 0.0
> >> f3.f31.\ Main 118 13970034 1.7 0.0 1.7 0.0
> >> f3.f31 Main 114 0 0.3 0.0 0.4 0.0
> >> f3.f31.\ Main 115 0 0.1 0.0 0.1 0.0
> >> ...
> >> Why f3.go consumes so much space (67.1%)? The only reason I can think of
> >> is IO Monad chain (>>) isn't space free as I thought.
> >>
> >> Did I get something fundamentally wrong?
> >>
> >> Thanks
> >> baojun
> >>
> >> _______________________________________________
> >> Haskell-Cafe mailing list
> >> Haskell-Cafe at haskell.org
> >> <javascript:_e(%7B%7D,'cvml','Haskell-Cafe at haskell.org');>
> >> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> >>
> >>
> >
> 
> -- 
> -- Dan Burton

> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe at haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe